1. Field of the Invention
The present invention relates to a prefilled syringe and to a production method for a barrel thereof and, more specifically, to a prefilled syringe excelling in gas barrier property and water vapor barrier property and to a production method for a barrel thereof.
2. Description of the Related Art
A prefilled syringe containing, in advance, a medication inside a barrel is prevailing recently for reasons such as savings of time of transferring the medication from a container to the syringe and a low risk of contamination by bacteria. A prefilled syringe with a non-breakable plastic barrel is generally used.
However, a prefilled syringe with a plastic barrel has problems such as deterioration of the medication caused by oxygen and evaporation of water from the medication. If the barrel is molded by a resin with barrier properties to avoid these problems, a problem such as elution occurs, involving another problem concerning safety. Therefore, a prefilled syringe with a plastic barrel is generally packaged along with a deoxidant or the like using an external packaging material made of a film which excels in gas barrier property or water vapor barrier property. The packaging step complicates production, and the packaging material makes storage cumbersome, taking significant space as a whole. Further, the packaging material and the deoxidant must be disposed of as waste after use, and it is hardly ecologically friendly. Further, in the case where only a heat-labile resin such as polyethylene can be used in order to prevent an interaction with the medication, the barrel itself may be deformed by high pressure steam sterilization.
Although a glass barrel does not have such faults as described above, it is brittle and variations occur in dimensional accuracy; hence it is not yet widely used.
There is also an invention of coating the whole outer wall surface of a barrel with a film having a gas barrier property. The film is made of materials, such as polyvinylidene chloride (PVDC), having a water vapor permeability of 20 g/m2·24 h (at 40° C., 90% RH) and may be deposited with aluminum. This prevents penetration of water vapor, oxygen, or the like through a wall surface into the barrel. Thus, the need for packaging the whole prefilled syringe along with a deoxidant or the like can be eliminated, thereby achieving a reduction in production steps as well as in storage space (see Japanese laid-open publication No. JP 11-332984 A).
Further, as an invention imparting a gas barrier property to a barrel itself, other than the invention of the above JP 11-332984 A, there is an invention in which 90% or more of an amorphous silicon oxide (SiOm) layer, which is obtained by baking a polysilazane film in an oxidizing atmosphere, is formed on a wall surface of the barrel at a thickness of 0.05 to 20 μm (see Japanese laid-open publication No. JP 10-57446 A).
In addition, there is an invention of obtaining a multilayer parison by sequentially and alternately injecting two or more kinds of molten thermoplastic resins into one mold with shifting injection timing from a molding machine having plural injection cylinders with one mold closing operation. Herewith, the multilayer parison, which is a preform for a hollow container, is sanitary and excels in gas permeability resistance and water permeability resistance. The multilayer parison can be obtained using a polyethylene terephthalate (PET) resin or a polyamide resin containing a meta-xylylene group as an intermediate layer and using the PET resin for inner and outer surface layers. A hollow container also usable for medical applications may be obtained by blow molding the multilayer parison (see U.S. Pat. No. 4,535,901).
However, although JP 11-332984 A does not mention a method of coating an outer wall of a syringe barrel with a film having a gas barrier property, an adhesive or a bonding layer is required for bonding the film on the barrel. In addition, it is difficult to coat the whole cylindrical barrel. When shrink packaging, the gas barrier property may not be ensured because the film and the syringe do not completely bond. Further, ethylene vinyl alcohol copolymer (EVOH), which is a typical gas barrier material, significantly degrades in barrier property by high pressure steam sterilization, so even if the outer wall of the barrel could be supposedly coated, it is pondered whether a desirable effect will be obtained.
On the other hand, when producing a barrel for a prefilled syringe using the method described in JP 10-57446 A, the method must go through 5 stages of the steps of (a) molding the barrel with a predetermined resin, (b) applying a polysilazane solution to the barrel, (c) removing an organic solvent in the polysilazane solution by drying in an oxygen atmosphere at 60° C. or less, (d) forming an amorphous silicon oxide layer by baking the barrel at a temperature of 60° C. to 200° C., and (e) forming a protective film with an epoxy resin or the like on the outermost layer. The production method is thus complicated, and it cannot be said that production efficiency is satisfactory. Further, polysilazane hydrolyzes when coming in contact with water and an alcohol solvent; therefore, an aromatic hydrocarbon such as xylene or petroleum ether must be inevitably used for a solvent. It takes time to completely remove those organic solvents, and in a case of incomplete removal thereof, a problem arises in terms of safety of the medication. Further, polysilazane produces pyrophoric silane gas, so control and handling thereof are difficult.
Further, the method described in U.S. Pat. No. 4,535,901 relates to a production method for a parison, which is a preform for a hollow container to be obtained by blow molding, and is not related to a barrel of a medical syringe with both ends opened and a production method thereof.